This invention is generally directed to developer compositions, and more specifically, the present invention relates to developer compositions with coated carrier components, or coated carrier particles that can be prepared by, for example, dry powder processes. More specifically, the present invention relates to compositions, especially carrier compositions comprised of a core and thereover certain polycarbonates, such as polycarbonate polymers formed by the thermal curing of cyclic polycarbonate oligomers and related oligomers with polar groups of, for example, tertiary amines or perfluorinated moieties incorporated to, for example, provide excellent acceptable charging characteristics for xerographic image development systems.
Advantages of the carriers of the present invention include in embodiments carrier coatings which are very robust, that is, they are substantially resistant to polymer fracture and subsequent chipping and delamination of the polymer from the core surface in, for example, high energy xerographic environments, that is, in which the energy imparted to the toner is about 0.5 W-hr per pound or higher, and which carriers additionally display a tribo charge of a positive value, for example from about a minus 35 to about a minus 40 microcoulombs per gram and a corresponding high negative tribo charge to the toner, excellent admix, for example, from about 1 to about 30 seconds as determined in a charge spectrograph, and the like. More specifically, the toner tribo can be, it is believed, from about a minus 5 to about a minus 50 microcoulombs per gram, from about a minus 25 to about a minus 45 microcoulombs per gram, or from about a minus 35 to about a minus 40 microcoulombs per gram, and more specifically, preferably, for example, about 15 to about 25, with corresponding positive tribo charges for the carrier. The tribo charges can be determined by a number of known methods, such as the use of a Faraday Cage.
Other advantages of the present invention include increased resistance of the carrier to mechanical aging in a xerographic environment and a decreased sensitivity of the carrier triboelectric value to the relative humidity of the environment. With respect to high toner tribo charge of a negative value, this property is important to xerographic, especially color applications, primarily because there is enabled development of toner particles into regions of the imaging member, such as a photoreceptor where strong fringe electrical fields exist, that is, at the borders of solids areas and lines. Developing toner particles through these fringe fields minimizes or eliminates the untoned part of the image which appears between two adjacent colors in an image.
The carrier particles of the present invention can be selected for a number of different xerographic copiers and printers, such as high speed color xerographic copies, printers, digital copiers, and more specifically, wherein colored copies with excellent and substantially no background deposits are achievable in copiers, printers, digital copiers, and the combination of xerographic copiers and digital systems. Developer compositions comprised of the carrier particles illustrated herein and prepared, for example, by a dry coating process are generally useful in electrostatographic or electrophotographic imaging systems, especially xerographic imaging and printing processes, and digital processes. Additionally, the invention developer compositions comprised of substantially conductive carrier particles are useful in imaging methods wherein relatively constant conductivity parameters are desired. Furthermore, in the aforementioned imaging processes the triboelectric charge on the carrier particles can be preselected depending on the polymer composition and dispersant component applied to the carrier core and the type and amount of the conductive component selected.